This invention relates to an automated production system for manufacturing semiconductor devices, and to a method of manufacturing semiconductor devices with at least a partially continuous production line.
Generally, a plurality of semiconductor devices, or chips, are formed in a semiconductor wafer through the use of a series of process steps such as epitaxial growth, oxidation, resist treatment including application of resist, exposure to light, development and etching, impurity doping by thermal diffusion or ion injection, gas-phase growth of polycrystalline silicon, silicon nitride film, and silicon oxide film, etc., forming of electrodes and lead wires, and so on.
Heretofore, a production system for manufacturing semiconductor devices has been automatized in each process step and in each connection between one process step and another process step. However, in the prior art, the automated production system has concentrated only on the yield for each process step. Therefore, a wafer which is not out of specification but is at a position off the central value of the specification in one process step is handed over to the next process step without any information concerning its being off the central value. The wafer that is within the specification but is off the central value in the previous process step is treated in the next process step under the same conditions as wafers that are not only within the specification but are also within the central value of the specification in the previous step. Therefore, the wafer that is off the central value may become defective in the next or subsequent process steps. Then the overall yield would be reduced. If someone intervenes in the next process step in order to correct the wafer that is off the central value, dirt will be introduced through such intervention and that will lower the reliability of the products made from the water. The overall yield will be unfavorably influenced by the dirt.
Namely, the method of manufacturing semiconductor devices and the production system thereof which is used in the prior art are, as described, for example, in U.S. Pat. No. 3,751,647. This system is based on the technology of obtaining data on completed products after a final test and altering each of the process steps by analysing the data, or on the technology of obtaining data on the completed products and data on products that are in an intermediate process step and changing the process step. Both technologies have a system of changing the conditions of a preceding process step after inspection, but the data of the inspection is not conveyed to the next process step. Accordingly, a product that is within the specification but off the central value in one process step will not be given any special treatment in the next process step to compensate for the deviation from the central value, and the deviation is carried on until the final process step, if the product is capable of reaching it.